I don't think there is anything wrong with someone fumbling over a few words in an 8 minutes speech! Everyone does, including politicians.
The Queen must now be slower and stooped physically, but she doesn't seem to wind down mentally at all. She still has a very commanding voice when reading speeches.
It was the first time I followed the State Opening live on the BBC and I really liked the commentary : it was entertaining, informative and respectful, but with a little bit of mischief and distance too. Just great !